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The fertility tradeoff

In Hamlet’s famous soliloquy, “To be or not to be – that is the question,” the Shakespearian character toys with the idea of suicide. He doesn’t know what the consequences will be, which makes the decision all the more harder. Is there an afterlife? Would it be braver to deal with the misfortunes of life without trying to escape them through death?

Most of the decisions you make, thankfully, are not matters of life or death. But there are tough ones, nonetheless, that impact the financial health of your business.

For instance, you can change the diet of your cows to boost fertility, but that could have a negative impact on milk fat.

Is this a Shakespearian dilemma for your cows? It doesn’t have to be.

Promising new developments

Fertility in U.S. dairy herds could use some help. It’s been stable the past 10 years, following earlier declines, but nothing to get excited about.

Now, there is promising research on the table. According to an article in the September 2011 edition of Theriogenology, feeding unsaturated fatty acids, such as linoleic acid, may be able to improve cows’ energy status for reproductive functions.

A study in the March 2011 Journal of Dairy Science found that cows fed a safflower oil supplement high in linoleic acid had greater concentrations of glucose, insulin-like growth factor-1 and progesterone in the blood. Glucose and insulin-like growth factor-1 are biological markers indicating improved energy status. That, in turn, may explain why the cows fed the supplement returned to ovulation sooner than control cows, which might give them a better chance of getting pregnant earlier in lactation.

Certain cautions

When supplying unsaturated fatty acids, such as supplements rich in linoleic acid, there are potential tradeoffs in terms of milk fat synthesis, acknowledges Jose Santos, dairy scientist at the University of Florida.

It depends on what else is being fed in the diet.

If the cows are being fed high-starch diets, or there is insufficient forage fiber, it can create acidic conditions in the rumen, which alters the microbial population and a digestive process known as biohydrogenation. When this occurs, the unsaturated fatty acids in the feedstuffs may be transformed into intermediate compounds that have a negative impact on milk fat synthesis.

Therefore, when feeding linoleic acid or other Omega-6 fatty acids, it is important to:

• Stay within a certain time window. Depending on the fat source, start supplementation three weeks prepartum in small quantities. Since cows aren’t milking yet, it won’t have an effect on milk fat synthesis. During the first two to three weeks post-partum, milk fat is naturally high, so the impact on milk fat synthesis will be less noticeable. Then, up to breeding time, producers are unlikely to notice any significant amount of milk fat depression if low to moderate amounts of the supplements containing unsaturated fatty acids are fed, Santos says.

• Restrict the supplemental fatty acid source to 1.2 to 1.5 percent of total diet dry matter intake. So, if cows are eating 54 to 55 pounds of daily dry matter, they should not be fed more than 0.5 to 0.75 pound from the supplemental source. Have your nutritionist balance this against the other fat sources in the diet.

• Finally, make adjustments in the ration that avert a possible negative shift in the biohydrogenation pathways in the rumen. Anything you can do to keep rumen pH from dropping, such as not overfeeding starch and having sufficient forage fiber, will help.